Field of the Invention
The present invention relates to an Equipment Front End Module (EFEM) including a wafer transfer chamber, load ports, and buffer stations.
Description of Related Art
In semiconductor manufacturing processes, wafers are handled in a cleanroom in order to achieve high yields and high quality. In current circumstances of the increase in device packaging density, the downscaling of circuit features, and the increase in wafer sizes, it is, however, difficult to control fine dust in an entire clean room both technically and costwise. Instead of improving cleanliness in the entire cleanroom, the “minienvironment system” for improving the cleanliness only in a local space around wafers has, therefore, been recently introduced into tools for performing processes including a wafer transfer process. An Equipment Front End Module (EFEM) plays a key role in the minienvironment system. The EFEM is a module in which a load port that can load thereon a container or so-called Front-Opening Unified Pod (FOUP) for transferring and storing wafers in an ultra clean environment and a wafer transfer chamber are adjacently disposed in the front-rear direction of the wafer transfer chamber.
The EFEM is configured so that a door part of the load port and a door provided on the front surface of the FOUP are in close contact and opened simultaneously, and so that a wafer transfer robot provided in the wafer transfer chamber can unload wafers from the FOUP and store the wafers in the wafer transfer chamber or can store the wafers unloaded from the wafer transfer chamber in the FOUP through the load port.
The load port is disposed in front of the wafer transfer chamber and the wafers transferred from the FOUP into the wafer transfer chamber by the wafer transfer robot through the load port undergo various processes and working in semiconductor processing equipment disposed in back (rear) of the wafer transfer chamber and are then stored again in the FOUP back from the wafer transfer chamber through the load port.
A configuration is also known in which a buffer station on which wafers can be temporality placed is disposed on a side surface of the wafer transfer chamber with the aim of improving the wafer handling capacity of the whole EFEM (see Japanese Patent Laid-Open No. 2008-27937). An interior space of the buffer station in which a plurality of wafers can be stacked at a predetermined pitch in a height direction communicates with the interior space of the wafer transfer chamber. The wafer transfer robot disposed in the wafer transfer chamber can store wafers in the interior space of the buffer station or can unload the wafers from the interior space of the buffer station. The configuration in which such a buffer station is disposed on each side surface of the wafer transfer chamber would allow more wafers to be stored than a configuration in which a buffer station is disposed at only on one side surface of the wafer transfer chamber.
The number of wafers that one buffer station can store is limited by the size of the buffer station. There are demands from EFEM installed plants for handling as many wafers as possible in a single EFEM. In order to meet the demands, it is conceivable to increase the height dimension of each buffer station to increase the storage space of the buffer station, thereby increasing the number of wafers that the buffer station can store.
However, the larger the height of a buffer station, the longer the up-down stroke (vertical travel distance) of the wafer transfer robot, which disadvantageously increases the size of the wafer transfer robot. The increase in the size of the wafer transfer robot causes an increase in the size of the wafer transfer chamber in which the wafer transfer robot is disposed inside and an increase in the footprint (installation area) of the whole EFEM. Therefore, it is desirable to avoid the increase in the size the wafer transfer robot as much as possible. Furthermore, the longer up-down stroke of the wafer transfer robot increases the time required for transferring each wafer unless the speed of operation of the wafer transfer robot is set higher than the conventional speed. Therefore it is not the best possible solution to increase the storage space of the buffer station in the height direction which entails the increase of the up-down stroke of the wafer transfer robot.
The size of wafers handled in the EFEM is standardized in the SEMI (Semiconductor Equipment and Materials International) standards. In order to improve productivity, the diameter of wafers has been increased and the transition from 300-mm-diameter (150-mm-radius) wafers to 450-mm-diameter (225-mm-radius) wafers is in progress. As the diameter of wafers increase, the weight per wafer increases. Accordingly, the strength of the wafer transfer robot needs to be enhanced. The strength of the wafer transfer robot may be enhanced by increasing the size of the wafer transfer robot.
However, as described above, it is desirable to minimize the increase in the size of wafer transfer robot which entails the increase of the footprints. There are demands from EFEM installed plants for handling 450-mm-diameter wafers with wafer transfer robots that conform to the same or substantially the same specifications as those for conventional wafer transfer robots that can transfer 300-mm-diameter wafers.
Note that the distance between adjacent wafers in the height direction (wafer slot pitch) when 450-mm wafers are stored in the FOUP or buffer station in the height direction according to the SEMI standards is set to a value greater than the wafer slot pitch adopted when 300-mm wafers are stored. The height dimension required for storing the 450-mm-wafers is larger than that required for storing the 300-mm wafers if the number of wafers is the same. To provide the wafer slot pitch as described above, it is inevitable from a design viewpoint to extend the storage space of the buffer station in the height direction. However, it is desirable to avoid increasing the height dimension of the buffer station due to reasons other than the wafer slot pitch. This is because the increase of the height dimension possibly causes the increase in the size of the wafer transfer robot and the increase in the footprint as described above.
The present invention has been made in light of these problems and a primary object of the present invention is to provide an EFEM that has a configuration capable of preventing or minimizing an increase in the up-down stroke distance of a wafer transfer robot (increase in the size of the wafer transfer robot) and an increase in the footprint of a whole EFEM and yet is capable of handling many wafers while adapting to an increase in the diameter of wafers.